Streamlining of high-performance cars at times poses conflicting requirements: high-speed cornering requires a negative-lift aerodynamic force on the car body to increase the vertical load and hence the cornering force of the tires, which, however, is accompanied by drag which limits the maximum speed achievable. Good road-holding and low drag can be achieved using adjustable streamlining surfaces, which change shape as a function of the speed of the car. More specifically, at very high speeds, never encountered when cornering, they are positioned to minimize drag, whereas, at lower speeds, they are positioned to maximize negative lift and so achieve maximum road-holding performance.
Adjustable streamlining surfaces, however, may pose numerous drawbacks: to be effective, they often must be fairly large, which normally conflicts with aesthetic requirements; they may require a mechanically strong, and therefore heavy, high-cost, support and actuating system to withstand aerodynamic stress; and, finally, being exposed to weather, they may call for fairly frequent maintenance to ensure consistent performance.
To alter the streamline configuration of a car at high speed, it has also been proposed to use air jets which interact with the airflow about the car. In other words, by blowing air through the car body, it is possible to interact with the airflow about the car to reduce the form drag component and so alter the streamline configuration of the car as a function of operating conditions, without actually altering the external shape of the car.
Examples of high-performance cars with high-speed streamline configuration-altering air jets are described in U.S. Pat. No. 5,863,090A1, U.S. Pat. No. 5,842,734A1, U.S. Pat. No. 5,908,217A1, U.S. Pat. No. 5,407,245A1, U.S. Pat. No. 6,033,010A1 and DE19633205A1, which are incorporated by reference.
Known air jet systems, for altering the streamline configuration of a car at high speed, however, may be bulky and heavy, and so increase weight—often a serious drawback in the case of high-performance cars—and may reduce the space available inside. Moreover, power consumption by the air fans employed is typically far from negligible, and is subtracted from the drive wheels. And finally, electric fans may call for oversizing the alternator on the car, thus further increasing overall weight.